This invention relates to a grate cooler with a cooling grate through which cooling gas flows and over which the cooling feed material, such as hot cement clinker, can move.
Grate coolers are used in the nonmetallic mineral industry for the rapid cooling of material previously burned in a furnace, such as for example cement clinker or other mineral materials, by cooling such material immediately thereafter on the cooling grate of the grate cooler. Along with traveling-grate coolers, devices widely used to convey hot feed material through the cooling region of the cooler include reciprocating-grate coolers, in which the grate system includes a multiplicity of alternately fixed and moving grate-plate carriers, to each of which are attached a plurality of grate plates provided with cooling air holes and through which cooling air flows substantially upwardly from below. As viewed in the conveyance direction of such coolers, fixed rows of grate plates alternate with rows of reciprocatingly movable grate plates, which are collectively attached, via their correspondingly reciprocatingly movably supported grate-plate carriers, to one or a plurality of longitudinally movably supported driven thrust frames. By virtue of the collectively oscillatory motion of all movable rows of grate plates, the material to be cooled, for example the hot cement clinker, is conveyed in pushing fashion while being cooled. In order to protect the grate plates from thermal-mechanical overloading, it is known to provide the plate tops with troughs or pockets for the accommodation and retention of cooling feed material, which then forms a protective bed for the hot feed material being cooled, which slides thereover. Such pockets are shown in European patent EP 0634 619 B2 issued to G. Dittman et. al. on Mar. 10, 1999 for a Grate Plate for a Grate Plate Cooler.
European patent EP 0718 578 A2 of T. Enhegaard published Jun. 26, 1996 for Method and Cooler for Cooling Particulate Material discloses a grate cooler in which the cooling grate, through which cooling air flows, does not move, but in which a row of reciprocatingly movable beam-shaped conveying elements is arranged transversely to the material conveyance direction above the grate surface. The material in the bed of material to be cooled is said to be moved successively from the beginning of the cooler to the end of the cooler by the reciprocating motion of the beam-shaped conveying elements. The wear problem occurring particularly in the reciprocating-grate cooler, especially in the overlap region of adjacent moving and fixed rows of grate plates, and resulting from cement clinker abrasion and sticking of material in the overlap region of the grate plates, is claimed to be reduced in this type of grate cooler.
It is an object of the invention to create an improved grate-cooler which is relatively simple in construction, has a cooling grate largely protected against wear, and can be operated in simple manner with a high cooling efficiency.
In the grate cooler of this invention, the cooling grate is stationary, that is, it does not include any moving parts. A plurality of rotatably supported tubular shafts, spaced apart from one another, are arranged transversely to the conveyance direction of cooling feed material above the stationary cooling grate, and attached to the side of the tubular shafts turned away from the stationary cooling grate are upwardly extending shovel arms, which execute a reciprocating oscillatory motion in the conveyance direction of cooling feed material. These shovel arms, acting as one-armed levers, which have a pushing surface on their forward side and a wedge surface on their rearward side, lie with their pushing surface in the hot bed of cooling feed material, and in their forward and backward oscillation they move the hot bed of cooling feed material successively from the cooling-grate beginning to the cooling-grate end. For protection against overheating by the hot clinker bed, a cooling medium such as, for example, cooling air flows through the hollow shafts supporting the shovel arms, this cooling medium being able to flow into the bed of cooling feed material via holes distributed about the circumference of the tubular shaft, and there to effect additional cooling of the cooling feed material.
Because the cooling grate is stationary and includes no moving parts, it is especially advantageous to provide the cooling grate with grate plates or regions with troughs for cooling feed material or pockets for cooling feed material in order to hold and retain cooling feed material so that, in the operation of the grate cooler, a lower, precooled bed of material or guard bed is formed on the stationary cooling grate, over which bed the hot material to be cooled is moved by the oscillating shovel arms. The bearings and the oscillatory drive or oscillatory drives of the shafts occupied by the shovel arms are advantageously arranged outside the lateral walls of the cooler in a manner protected from the hot cooling feed material.
According to a further feature of the invention, the pivot angle between the pushing surface of the oscillating shovel arms and the cooling-grate plane covers a range from about 160xc2x0 to about 90xc2x0, that is, a differential pivot-angle range of about 70xc2x0. This means that the pushing surfaces of the oscillating shovel arms can move the hot cooling feed material obliquely upwardly, up to approximately parallel to the cooling-grate plane, in the conveyance direction of cooling feed material, that is, the limitation of the forward oscillatory motion prevents the cooling feed material from being pressed against the cooling grate by the pushing surfaces of the shovel arms. At the same time, the oscillatory motion of the shovel arms causes frittings-together or agglomerations of the hot cooling feed material, such as for example cement clinker, to be broken up again by the shovel arms without the shovel arms being conveyed into the lower, colder bed of cooling feed material. The height of the oscillating shovel arms, that is, the radial extent of the one-armed lever arms, can be different; for example, especially high shovel arms can be used in the initial region of the grate cooler in order to promote the effect of breaking up agglomerations of cooling feed material. Thus an intermediate crusher, for example in the form of crushing rolls, often used previously in a grate cooler of conventional design, can be omitted.